An engine-driven compressor having a compressor body driven by an engine enables compressed air to be obtained even in situations in which it is difficult to secure power supply. In particular, package-type engine-driven compressors, in which a compressor body, an engine, and other required equipments have been integrated together and accommodated in a soundproofed box, are widely employed as compressed air supply sources in civil engineering and construction field or sites and the like due to their ease of transport and installation.
Since diesel is superior to gasoline in its fuel consumption and gas mileage, a diesel engine is typically used as an engine for driving the compressor body in such engine-driven compressors for saving running costs.
However, because of their structure, diesel engines emit a larger amount of PM together with exhaust gas upon combustion as compared with gasoline engines. Since PM causes air pollution and health hazards, regulation values (mass per unit output [g/kWh]) for PM emitted from a diesel engine are determined by emission gas regulation. To adapt to this emission regulation, aftertreatment apparatuses with a diesel particulate filter (hereinafter referred to as a “DPF”) are installed in exhaust gas paths of diesel engines in order to reduce the emission amount of PM.
Since the DPF collects PM in exhaust gas by the built-in filter material in order to reduce the emission amount of PM, with continuous use, the deposition of PM with respect to the filter element proceeds and eventually clogs the filter element. Increase in the resistance for the exhaust gas due to the clogging of the DPF results in lowering the engine output and deteriorating fuel efficiency. Thus, it requires a process to regenerate the filter element by removing PM deposited on the filter element.
As an exemplary method for regenerating the filter element, a continuous regeneration type DPF in which an oxidation catalyst is accommodated at an entrance side of the DPF and the filter element is accommodated at a downstream of the oxidation catalyst has been suggested. This continuous regeneration type DPF is continuously burning and removing PM by means of the heat of the exhaust gas while the engine is running, in which NO2 is generated by the action of an oxidation catalyst when heated to its activation temperature or more by the exhaust gas during operation of the engine, and the NO2 can be used as an oxidizer in burning of PM so as to regenerate the filter element at a temperature lower than that at which the PM burns by itself with oxygen.
However, even in the above continuous regeneration type DPE, when the engine runs for a long time with the temperature of the exhaust gas below the activation temperature of the oxidation catalyst, such as when the engine runs under a low load for a long time, NO2 is not generated and the FM cannot be burned. Consequently, the deposition of PM with respect to the filter element proceeds. Once the engine transits to high-load operation after PM is deposited with respect to the filter element beyond a certain amount and the resistance for the exhaust gas is thus elevated, the elevated resistance for the exhaust gas increases the temperature of the exhaust gas to higher than that in normal high load operation. As a result, a large amount of PM deposited in the filter element starts to burn by themselves so as to emit high heat, which causes cracks or melts in the DPF body and the filter element (hereinafter referred to as the filter element or the like) accommodated in the DPF.
Therefore, even in the continuous regeneration type DPF, when the deposition amount of PM with respect to the filter element becomes or exceeds a predetermined amount, a temperature of the exhaust gas is increased by additionally injecting fuel or delaying the injection timing and thus a temperature of the oxidation catalyst in the DPF is increased, so that PM deposited on a filter element is forcibly burned with NO2 as an oxidizer ((Patent Document 1).
It should be noted that, although not disclosing configuration related to a DPF, Patent Documents 2 and 3 disclose inventions related to methods for controlling running of engine-driven compressors.
The engine-driven compressors described therein perform capacity control and speed control during running to supply compressed air at a certain pressure to the consumption side with low fuel consumption (Patent Documents 2, 3).
The capacity control thereof is control to open an inlet port of a compressor body and to transition into loaded running in which intake and compression of air is performed when pressure at a discharge side of the compressor body falls to below a predetermined set pressure due to consumption of compressed air, and to close an inlet port of a compressor body and to transition into unloaded running in which intake and compression of air is stopped when pressure at the discharge side of the compressor body reaches the predetermined set pressure or greater.
Moreover, the speed control is control to raise the rotational speed of the engine as pressure at the discharge side of the compressor body falls, and to decrease the rotational speed of the engine as pressure at the discharge side of the compressor body rises.
It should be noted that in the engine-driven work machine described in the Patent Document 3, when in the above-mentioned unloaded running in which the inlet port of the compressor body is in a closed state, there is a proposal to reduce the load on the engine during the unloaded running by releasing the pressure on the discharge side of a compressor body to the atmosphere, or by introducing the pressure on the discharge side to an inlet passage of an inlet valve.